(1) Field of the Invention
The invention relates to a method and a device for localization of the position of a wheel of a vehicle equipped with an electronic box suited for transmitting, upon receiving an identification request signal whose power is greater than a predetermined detection threshold, signals representing operational parameters of said wheel comprising, further, an identification code for the latter, and directed at a central unit mounted on the vehicle.
The invention extends further to localization methods combining the method according to the invention and possible other methods of localization for performing the localization of all of the wheels of a vehicle It also extends to localization devices implementing such localization methods.
(2) Description of the Related Art
For safety reasons, more and more motor vehicles have monitoring systems comprising electronic boxes provided with sensors mounted on each of the wheels of the vehicle, which sensors are dedicated to the measurement of parameters such as pressure or temperature of the tires equipping these wheels, and are intended to inform the driver of any abnormal variation of the measured parameter.
These monitoring systems are conventionally provided with an electronic box mounted on each of the wheels of the vehicle and comprising a temperature and/or pressure sensor, a microprocessor and a radiofrequency transmitter (or RF transmitter), and a central unit for receiving signals transmitted by the transmitters, comprising a calculator integrating a radiofrequency receiver (or RF receiver) connected to an antenna.
One of the problems requiring resolution for such monitoring systems resides in the obligation of having to associate each signal received by the receiver in the central unit with information concerning the location of the box which transmitted the signal and therefore of the wheel at the origin of this signal; this obligation continues during the lifetime of the vehicle, that is to say it must be respected even after changing wheels or more simply rotation of the position of the wheels.
Currently, a first method of localization consists of using three low frequency antennas each positioned near one of the wheels of the vehicle and performing a localization procedure consisting of successively exciting each of these three antennas by the transmission of a low-frequency magnetic field.
According to this method, the sensor mounted on the wheel located near the excited antenna orders—in response to and directed at the central unit—the transmission of a low-frequency signal comprising an identification code of said sensor, such that successive excitation of the three antennas leads to the localization of the three electronic boxes mounted on the wheels adjacent these antennas, and by deduction, to the localization of the fourth box.
The principal advantage of such a method resides in the fact that the localization procedure is very fast and leads to a nearly instantaneous localization after starting the vehicle.
In contrast, this solution requires equipping the vehicle with three antennas with all the associated constraints: connection cables, command amplifiers, etc. which means that it proves costly.
This disadvantage concerning the installation cost of the means for implementing the localization method can be resolved when the vehicle is equipped with a hands-free access device intended to enable access to said vehicle and to start the latter.
Specifically, the solution then consists—as in particular described in the patent application WO 02/051654—of using transmitting antennas along with their power supply means incorporating a step-up transformer, for this hands-free access device, for implementing the wheel localization procedure.
As described in the aforementioned patent application, the implementation of this solution consists, for example, of commanding the transmission by the transmitting antennas of an uncoded signal when said antennas are used for localization of the wheels, and commanding the transmission of a coded signal during the use of the antennas for their original purpose of checking vehicle access.
Such a solution very attractive in theory proves in contrast very awkward to implement in practice. Specifically, the antennas for the hands-free access devices are not ideally positioned in order to enable the localization of the wheels of a vehicle.
Further, the cost of the “antennas/step-up transformer” assembly makes this solution inapplicable to a car not having a hands-free access device.
In conclusion, each of the two principal solutions currently implemented with a view to localizing the wheels of a vehicle firstly have a number of specific disadvantages and secondly offer no flexibility of use.